Magnetic biomonitoring of atmospheric dust using tree leaves of Ficus benjamina in Querétaro (México).

There are limited economic and reliable tools to monitor the effects of airborne particulate matter PM originating from rapid industrialization, urbanization, population growth, and economic development. It is now well established that urban PM contains magnetic particles along with other air pollutants. The velocity and temporal variability of the deposition of such PM on tree leaves are subject to the pollution sources, climate, and local atmospheric conditions. Therefore, these variables have to be taken into account during a biomonitoring. This study presents a magnetic biomonitoring in the city of Querétaro. In the city's metropolitan area, the most abundant and perennial tree species for biomonitoring is Ficus benjamina. For leaves of this species, the number of days needed for collection NDNC was measured, taking into account the meteorological conditions and the time at which they reached the saturation of airborne PM (pollutants). By means of sequential sampling, we identified that the minimum NDNC after a rainfall > 3 mm is 15 days. In such a period, total suspended particle TSP depositions reach its dynamic equilibrium. This behavior can be observed from measurements of specific magnetic susceptibility χ in Ficus benjamina samples and their comparison with TSP depositions collected with traditional Hi-Vol monitoring systems. After the NDNC calculation, a magnetic monitoring was performed with the biomonitor Ficus benjamina to evaluate the air quality at different sites in the metropolitan area every month for a period of 5 months. Values of χ ranged from 0.45 to 18.52 × 10-8m3kg-1. The species Ficus benjamina can be used as a biomonitor in the city of Querétaro only in seasons (winter-spring) with no or low rainfall. The species has the advantage of providing current PM information about a specific period of time.

Magnetic parameters as proxies for anthropogenic pollution in water reservoir sediments from Mexico: An interdisciplinary approach.

We assess the element pollution level of water reservoir sediments using environmental magnetism techniques as a novel approach. Although "La Purísima" Water Reservoir is an important source for multiple activities (e.g. recreational, fishing and agricultural) in Guanajuato state, it has been receiving for the last centuries a high load of pollutants by mining extraction, urbanization and land-use change from the Guanajuato Hydrological Basin. The analyses of environmental magnetism, geochemistry, X-ray energy dispersive spectroscopy, scanning electron microscopy and multivariate methods were applied to study sediments from the reservoir and basin. Accordingly, they indicate the presence of iron oxides (magnetite and hematite) and iron sulfides (pyrite and greigite), which evidences relevant differences in particle size and concentration within the water reservoir (median mass-specific magnetic susceptibility χ = 23.2 × 10-8 m3/kg), as well as with respect to the river basin sediments (median χ = 88.8 × 10-8 m3/kg). The highest enrichment factor EF values (median values of EF = 2-10 for As, Co, Ba, Cu, Cd, Ni and EF > 20 for S) are mainly associated with historical mining activities that have led to an enrichment of potentially toxic elements on these water reservoir sediments. We propose the use of concentration and grain size dependent magnetic parameters, i.e. χ, remanent magnetizations and anhysteretic ratios ARM/SIRM and χARM/χ, as proxies for Ba, Co, Cr, Ni, P and Pb pollution in these river and water reservoir sediments. Such parameters allow to evaluate this sedimentary environment, and similar ones, through useful and convenient proxies.

An environmental magnetism approach to assess impacts of land-derived sediment disturbances on coral reef ecosystems (Cartagena, Colombia).

We used environmental magnetism methods to study recently deposited marine sediments from the estuarine ecosystems on the Caribbean coast of Colombia. Cartagena region has undergone an increasing sediment load during the last decades via sediment plumes from Magdalena River and its distributary man-made channel. Concentration dependent magnetic parameters show an increasing abundance of ferrimagnetic minerals on the uppermost sediments on sites located close to the continent (remanent magnetization SIRM = 5.4-9.5 × 10-3Am2 kg-1) as well as faraway sites (SIRM = 0.5-1.7 × 10-3Am2 kg-1 near Rosario Islands coral reef complex). The magnetic grain size and mineralogy along the cores are variable, showing the dominance of the magnetite-like minerals (remanent coercivity Hcr = 34.3-45.3 mT), with a minor contribution of high-coercivity minerals (Hcr = 472-588 mT). In addition, there is a moderate enrichment of elements Cu, Mo, and Zn (enrichment factor EF = 1.5-3.8) that indicates the additional land-derived contribution on sediments. The environmental magnetism approach, which shows significant signals of magnetic minerals and trace elements, is a reliable tool to prove the presence of continental sediment supply in coral reef ecosystems.

Biomonitors of urban air pollution: Magnetic studies and SEM observations of corticolous foliose and microfoliose lichens and their suitability for magnetic monitoring.

This study explored the suitability of available lichen species as air pollution biomonitors and assessed their potential for magnetic monitoring in cities. Several lichens on tree bark were collected in urban and industrial sites from Tandil city, as well as control sites. The results showed that magnetite-like minerals were the main magnetic carriers in all sites and samples. However, the concentration varied between clean and polluted sites. In addition, magnetic-grain size-distribution showed clear differences between sites. Observations by scanning electron microscopy showed different particles in a variety of shapes and grain sizes; moreover, the presence of iron oxides and several toxic elements was detected by energy dispersive spectroscopy analysis. Although eleven lichen species were identified that appeared suitable for use as air-pollution monitors, three of them, Parmotrema pilosum, Punctelia hipoleucites and Dirinaria picta, occurred more frequently in the area, thus constituting appropriate species for future monitoring in the study area.